1. Field of the Invention
This invention relates to determining the existence and/or a property (such as the location) of a contact such as a ball bounce in a sporting activity or the like.
2. Background of the Invention
The invention has been particularly developed for determining the location of the bounce point of a tennis ball in relation to the court line markings so as to enable objective determination whether the preceding tennis stroke has complied with the rules of tennis or whether the point of bounce is outside of the relevant court lines. The invention, however, is not limited to this particular field of application. For example the invention can be used in cricket to determine if the ball has contacted the edge of the cricket bat before being caught by a fieldsman and hence to determine objectively if the batsman has been dismissed under the rules of cricket. The invention may also be useable with other sporting, game, recreational, or entertainment activities where parameters of a contact can be relevant to some aspect of the activity Examples only of such activities and such contacts include:                in the sport of basketball where contact of a player with a part of an opponent's body may constitute a foul under the rules of basketball;        in the sport of boxing a contact involving the gloved fist of a boxer against allowable parts of the body of the opponent may score points for the boxer, or contacts and other parts of the opponent's body may incur penalties or warnings under the rules of boxing;        in the sport of volleyball, simultaneous contact of the ball with two hands is required for a legitimate strike of the ball under the rules of volleyball;        in the sport of tennis, apart from legality of a shot depending on where the ball bounces, the nature of contact of the ball with the racket strings, e.g. to impart particular spin to tie ball, may be desirably monitored particularly in coaching of a tennis player;        in the recreation or entertainment of dancing or in the sport of gymnastics, the locations of foot falls on the arena surface of the participants may be desirably monitored particularly in training or coaching of such participants;        in motor car or motor cycle racing, the nature and location of the contact of the vehicle tyres with the road or track surface may be desirably monitored as indicative of the performance of the vehicle or behaviour of the driver/rider and this may monitoring be useful particularly in adjusting the technical features of the vehicle or in training or practice of the driver/rider;        in “Australian Rules” football, whether the ball has touched a goal post can determine the score awarded;        in soccer, hand contact with the ball to block or control its movement is mostly illegal so unambiguous detection of such an impact can be useful;        in baseball and softball whether or not a pitched ball has touched the bat before being caught by the catcher can determine the treatment of the pitch as a strike or as a “foul tip” which means that the batter is out.        
Although the invention will be particularly described herein primarily in relation to determining parameters of the bounce of a tennis ball occurring within a tennis game, it is to be understood that the invention is not limited to this particular field of application and, as outlined above, can be applicable to other sporting, game, recreational, and entertainment activities.
The determination of the point at which a tennis ball bounces in relation to the line markings or boundaries of the tennis court determines whether the stroke is called legal or is illegal or “out” according to the rules of tennis. Such calling of bounce points is a skilled exercise and in professional tournaments a central umpire and many lines persons located around the tennis court continuously monitor the bounce points to call the shots legal or “out”. There is much dissension evident in tennis tournaments concerning the validity of calls made by the umpire and lines persons.
To help alleviate such dissension some electronic aids have been proposed or used in the past. These have been based on one of three principles:
(1) Impact sensors placed within the court surface so that when a ball strikes the ground, the sensors at that location record the impact and the resulting signals can be monitored to determine objectively whether the bounce point was within or outside the court boundary lines.
(2) Light beams have been projected along and transverse to the tennis court in the vicinity of the boundary lines so that when the tennis ball strikes the surface and interrupts the beams, the exact location of the bounce point can be determined from the interrupted beams and hence an objective determination made whether the bounce point is within or outside of the court boundary lines—an apparatus based on this principle is used in some tournaments and is known by the trade mark “Cyclops”.
(3) Images of the tennis court and surrounds are captured by multiple cameras located at known positions wound the court and these cameras continuously capture images including images of the ball in flight which are then analysed to determine trajectories of the tennis ball enabling computation of bounce points by interpolation within the computed trajectories. A simulation of the ball bouncing on the court surface including location of any adjacent court boundary lines can then be displayed for a viewer of the display simulation to determine whether the bounce point was within or outside the court boundary lines. A system based on this general principle has been used in tournaments and is known as the “Hawk Eye” system,
These systems can have one or more limitations such as expense of the hardware systems and installations thereof; the difficulty and precision required in providing calibrating or testing and operating of such systems at a tennis venue; limitations on applicability throughout a tennis game since there can be many movements of bodies and many impacts on the court surface during a tennis game that can be registered by such apparatus and, unless accurately discriminated, could lead to false indications—for example the “Cyclops” system is generally used only for determining the bounce point of a tennis player's serve and not subsequent tennis shots.